Capacitor with high dielectric constant materials

ABSTRACT

A stabilized capacitor using non-oxide electrodes and high dielectric constant oxide dielectric materials is provided. The stabilized capacitor comprises a non-oxide electrode with an oxidized upper surface. A high dielectric constant oxide dielectric material is adjacent to the oxidized upper surface of the non-oxide electrode. An upper layer electrode is adjacent to the high dielectric constant oxide dielectric material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/903,160, filed Jul. 11, 2001.

BACKGROUND OF THE INVENTION

This invention relates generally to capacitors, and more particularly tocapacitors made with non-oxide electrodes and oxide dielectrics havinghigh dielectric constants but with reduced leakage current, and tomethods of making such capacitors and their incorporation into DRAMcells.

The increase in memory cell density in DRAMs presents semiconductor chipdesigners and manufacturers with the challenge of maintaining sufficientstorage capacity while decreasing cell area. One way of increasing cellcapacitance is through cell structure techniques, including threedimensional cell capacitors. The continuing drive to decrease size hasalso led to consideration of materials with higher dielectric constantsfor use in capacitors. Dielectric constant is a value characteristic ofa material and is proportional to the amount of charge that can bestored in a material when the material is interposed between twoelectrodes. Promising dielectric materials include Ba_(x)Sr_((1−x))TiO₃(“BST”), BaTiO₃, SrTiO₃, PbTiO₃, Pb(Zr,Ti)O₃ (“PZT”), (Pb,La)(Zr,Ti)O₃(“PLZT”), (Pb,La)TiO₃ (“PLT”), KNO₃, Nb₂O₅, Ta₂O₅, and LiNbO₃, all ofwhich have high dielectric constants making them particularly desirablefor use in capacitors. However, the use of these materials has beenhampered by their incompatibility with current processing techniques andtheir leakage current characteristics. The leakage currentcharacteristics of Ta₂O₅ on electrodes such as polysilicon, W, WN_(x),and TaN are not as good as those of the conventional silicon nitridecapacitor.

Leakage current is controlled not only by the quality of the Ta₂O₅dielectric film, but also by the state of the interface between theTa₂O₅ film and the electrodes. Attempts have been made to overcome theproblems associated with the use of Ta₂O₅. Some of the efforts havefocused on post-Ta₂O₅ treatments, such as annealing in the presence ofultraviolet light and ozone (UV-O₃ annealing), dry O₂ annealing, orrapid thermal nitridation (RTN), to repair the oxygen vacancies in theas-deposited chemical vapor deposited (CVD) Ta₂O₅, film by excitedoxygen or nitrogen atoms. Other work has focused on depositing speciallayers around the Ta₂O₅ film to prevent oxidation during laterprocessing. For example, U.S. Pat. No. 5,768,248 to Schuegraf involvesthe deposition of a dielectric nitride layer after the removal of anoxide layer on a capacitor plate. A Ta₂O₅ dielectric layer is thendeposited, followed by a second nitride layer. The nitride layerrestricts oxidation of the inner capacitor plate during subsequentannealing of the Ta₂O₅ layer. In U.S. Pat. No. 5,814,852 to Sandhu etal., a primarily amorphous diffusion barrier layer is deposited on theTa₂O₅ dielectric layer.

Chemical vapor deposited (CVD) Ta₂O₅ dielectric films are prepared in anoxygen gas mixture at elevated temperatures. Consequently, the bottomelectrode in a capacitor stack, onto which the Ta₂O₅ film is depositedtends to be severely oxidized by the process. This results in a highleakage current, as well as low capacitance.

Non-oxide electrodes have been shown to be promising electrodes for usewith high dielectric constant oxide dielectrics. However, the resultingleakage current is high for thinner films or layers of oxide dielectricssuch as Ta₂O₅. Therefore, there is a need for improved processes forincorporating non-oxide electrodes, such as TiN, TaN, WN, and W, andhigh dielectric constant oxide dielectric materials such as Ta₂O₅ andBa_(x)Sr_((1−x))TiO₃, in capacitor constructions having improved leakagecurrent and for capacitors containing these materials.

SUMMARY OF THE INVENTION

The present invention meets these needs by providing a stabilizedcapacitor using non-oxide electrodes and high dielectric constant oxidedielectric materials and methods of making such capacitors. By“non-oxide” electrode, it is meant an electrically conductive materialwhich does not contain any metal oxides. By “high dielectric constantoxide dielectric” materials we mean oxides of aluminum, barium,titanium, strontium, lead, zirconium, lanthanum, and niobium, including,but not limited to Al₂O₃, Ba_(x)Sr_((1−x))TiO₃ (“BST”), BaTiO₃, SrTiO₃,Ta₂O₅, Nb₂O₅, PbTiO₃, Pb(Zr,Ti)O₃ (“PZT”), (Pb,La)(Zr,Ti)O₃ (“PLZT”),(Pb,La)TiO₃ (“PLT”), KNO₃, and LiNbO₃ and having a dielectric constantof at least about 20.

In accordance with one aspect of the present invention, the methodincludes providing a non-oxide electrode, oxidizing an upper surface ofthe non-oxide electrode, depositing a high dielectric constant oxidedielectric material on the oxidized surface of the non-oxide electrode,and depositing an upper layer electrode on the high dielectric constantoxide dielectric material.

The surface oxidation of the non-oxide electrode can be carried out inan atmosphere containing an oxidizing gas such as O₂, O₃, H₂O, or N₂O ata temperature in the range of from about 250° to about 700° C. Theoxidation can be performed in the same reaction chamber as the step ofdepositing the high dielectric constant oxide dielectric material priorto depositing the high dielectric constant oxide dielectric material.Preferably, the oxidation is a gas plasma treatment which is carried outat a temperature in the range of from about 250° to about 500° C.,although other oxidation techniques such as furnace oxidation or rapidthermal oxidation (RTO) may be used. The high dielectric constant oxidedielectric material is selected from the group consisting of Al₂O₃,Ba_(x)Sr_((1−x))TiO3, BaTiO₃, SrTiO₃, Ta₂O₅, Nb₂O₅, PbTiO₃, Pb(Zr,Ti)O₃,(Pb,La)(Zr,Ti)O₃, (Pb,La)TiO₃, KNO₃, and LiNbO₃, and preferablycomprises either Ta₂O₅ or Ba_(x)Sr_((1−x))TiO₃.

Another aspect of the invention is a capacitor which includes anon-oxide electrode, the upper surface of which is oxidized. Thecapacitor includes a high dielectric constant oxide dielectric materialadjacent the upper surface of the non-oxide electrode, and an upperlayer electrode adjacent the high dielectric constant oxide dielectricmaterial. In a preferred embodiment, the non-oxide electrode ispreferably selected from the group consisting of TiN, TaN, WN, and W,and the high dielectric constant oxide dielectric material is selectedfrom Al₂O₃, Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃. The upper surface of thenon-oxide electrode is preferably oxidized using an oxidizing gas plasmasuch as O_(3.)

Another aspect of the present invention is a DRAM cell and method ofmaking it. In a preferred form, the method comprises providing anon-oxide electrode, oxidizing an upper surface of the non-oxideelectrode, depositing a high dielectric constant oxide dielectricmaterial on the non-oxide electrode, depositing an upper layer electrodeon the layer of high dielectric constant oxide dielectric material,providing a field effect transistor having a pair of source/drainregions, electrically connecting one of said source/drain regions withthe non-oxide electrode and electrically connecting the other of saidsource/drain regions with a bit line.

Accordingly, it is a feature of the present invention to provide astabilized capacitor having improved leakage current characteristicsusing non-oxide electrodes and high dielectric constant oxide dielectricmaterials, their incorporation into DRAM cells, and methods of makingsuch capacitors. These, and other features and advantages of the presentinvention, will become apparent from the following detailed description,the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic fragmentary sectional view of a semiconductorsubstrate fragment made according to one embodiment of the presentinvention;

FIG. 2 is a graph of sheet resistance and O₃ gas plasma treatment time;

FIG. 3 is a graph of leakage current density and capacitance for oneembodiment of the present invention;

FIG. 4 is a graph of leakage current density and capacitance for oneembodiment of the present invention; and

FIG. 5 is a diagrammatic fragmentary sectional view of anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a fragmentary view of a semiconductor substrate isindicated generally by reference numeral 10. As used herein, the term“semiconductor substrate” refers to silicon structures including siliconwafers, silicon structures in the process of fabrication, asemiconductor layer, including a semiconductor layer in the process offabrication, and the like. The semiconductor substrate 10 includes abulk silicon substrate 12 with a conductive diffusion area 14 formedtherein. An insulating layer 16, which is typically a borophososilicateglass (BPSG), is provided over substrate 12. There is a contact opening18 formed in the insulating layer 16 to diffusion area 14. A conductivematerial 20 fills contact opening 18 forming an electrically conductiveplug, with conductive material 20 and oxide layer 16 having beenplanarized using conventional techniques. Conductive material 20 can beany suitable material, such as, for example, tungsten or conductivelydoped polysilicon. A barrier layer (not shown) of a material such asTiAIN may be present at the top of the plug.

The plug of conductive material 20 can be produced by initially formingconductively doped polysilicon to completely fill opening 18. Thepolysilicon layer can then be etched back using wet or dry etchprocesses, or by chemical-mechanical polishing (CMP) such that allconductive material has been removed from the upper surface ofinsulating layer 16. Preferably, the removal technique causes a slightrecess of conductive material 20 within opening 18.

A capacitor construction generally indicated by reference numeral 22 isprovided on insulating layer 16 and plug 20, with conductive plug 20constituting a node to which electrical connection to capacitor 22 ismade. Capacitor 22 comprises a non-oxide electrode 24 which iselectrically conductive and has been provided and patterned over node20. Examples of preferred materials for non-oxide electrode 24 include,but are not limited to, TiN, TaN, WN, and W. Generally, non-oxideelectrode 24 has a thickness of from between about 200 to about 500Å.

The upper surface 26 of non-oxide electrode 24 is oxidized. Theoxidation can be carried out at low temperatures (e.g., from about 250°to about 700° C.) in an atmosphere containing O₂, O₃, steam (H₂O), orN₂O. The oxidation may optionally be performed in the same reactionchamber where the high dielectric constant oxide dielectric materialdeposition occurs. Such oxidation takes places using an extendedstabilization step under oxidizing conditions prior to deposition of thehigh dielectric constant oxide dielectric material. The oxidation ispreferably performed using a gas plasma at a temperature in the range offrom about 250° to 500° C. The oxidation forms a very thin layer ofoxidized material on the surface of the non-oxide electrode. Generally,the thin oxidized layer has a thickness of from about 10 to about 100Å.For example, depending on the original non-oxide material, the thinoxidized layer may comprise TiON, TaON, WON, and/or WO.

A layer of high dielectric constant oxide dielectric material 28 is thendeposited on the oxidized surface of non-oxide electrode 24. The highdielectric constant oxide dielectric material may be, but is not limitedto, Al₂O₃, Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃. One example of a process fordepositing a high dielectric constant oxide dielectric material such asAl₂O₃, Ta₂O₅ or Ba_(x)Sr_((1−x))TiO₃ includes using CVD techniques andmetalorganic precursors. Typically, such metalorganic precursors wouldbe flowed into a reactor at an appropriate rate under reduced pressureand elevated temperatures to form the dielectric layers 28 An upperlayer electrode 30 is then deposited on high dielectric constant oxidedielectric material 28.

Referring now to FIG. 5, another embodiment of the invention is shownwhich depicts the fabrication of DRAM circuitry. A semiconductorsubstrate 40 comprises two memory cells, each memory cell including acapacitor 42 and a shared bit contact 44. Capacitors 42 electricallyconnect with substrate diffusion regions 46 (source/drain regions)through silicide regions 48. For simplicity, capacitors 42 are shown ascomprising a first capacitor electrode 50 having a thin oxidized surface50 a, a capacitor dielectric 52, and a second capacitor electrode/cellplate 54. These layers are fabricated of the materials described above,including conductive non-oxide electrode materials and the highdielectric constant oxide dielectric materials. These layers areprocessed as described above to provide the capacitor structure of thepresent invention. A dielectric layer 56 is formed over second capacitorplate 54. A bit line 58 is fabricated in electrical connection with bitcontact 44. Word lines 60 are fabricated to enable selective gating ofthe capacitors relative to bit contact 44.

In order that the invention may be more readily understood, reference ismade to the following example, which is intended to be illustrative ofthe invention, but is not intended to be limiting in scope.

EXAMPLE

A metal-insulator-metal capacitor test chip was prepared. The bottomelectrode was a tungsten nitride (including WN, W₂N, WN_(x), ormixtures) film deposited using CVD techniques to a thickness of about450Å. Three slightly different WN_(x) films were prepared, each having adifferent nucleation stage and different step coverage (identified asCVD WN_(x) A, CVD WN_(x) B, and CVD WN_(x) C). The CVD WN_(x) films wereoxidized using a gas plasma generated from O₃ at 400° C. A film of Ta₂O₅having a thickness of about 80 Å was deposited on the plasma treated CVDWN_(x) films. The upper electrode was a TiN film about 400Å thickdeposited by physical vapor deposition (PVD) techniques. The capacitorwas patterned using a photomask.

FIG. 2 shows the sheet resistance of the CVD WN_(x) B film. The sheetresistance increased after gas plasma treatment, indicating that a thinlayer of WO_(x) formed at the film surface. The sheet resistanceincreased with increasing gas plasma treatment time. After about 30seconds of gas plasma treatment, the increase in sheet resistance beganto saturate, indicating that the formed passivation layer preventedfurther oxidation very effectively. The overall increase in sheetresistance after gas plasma treatment for 120 seconds was only about10%, indicating that the passivation layer was thin. The thinpassivation layer works to prevent further uncontrolled oxidation duringTa₂O₅ dielectric deposition and later thermal treatments. WO_(x) has avery high dielectric constant (300), and therefore will not reduce thecapacitance of the device.

FIG. 3 shows a comparison of the leakage current density and capacitanceof CVD WN_(x) B bottom electrode wafers which were untreated, gas plasmatreated with O₃, and gas plasma treated with NH₃. The electrical datawas measured at 85° C., with the leakage current density measured at +1V and the capacitance at 0 V. The O₃ plasma treated capacitor had thelowest leakage density, but the capacitance was not reduced.

FIG. 4 shows a comparison of the leakage current density and thecapacitance of the CVD WN_(x) C bottom electrode wafers which wereuntreated, and gas plasma treated with O₃. Again, the O₃ plasma treatedcapacitor had lower leakage density, but the capacitance was notreduced.

While not intended to be limited to any theory, it is believed that theformation of the thin oxide layer reduces the interface defects betweenthe non-oxide bottom electrode and the high dielectric constant oxidedielectric material, providing reduced leakage current without severedegradation in dielectric capacitance because the thin oxide layeritself has a high dielectric constant.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes in the methods and apparatusdisclosed herein may be made without departing from the scope of theinvention, which is defined in the appended claims.

What is claimed is:
 1. A capacitor comprising a substrate, a non-oxideelectrode having an oxidized upper surface adjacent said substrate, ahigh dielectric constant oxide dielectric material adjacent saidoxidized upper surface of said non-oxide electrode, and an upper layerelectrode adjacent said high dielectric constant oxide dielectricmaterial.
 2. A capacitor as claimed in claim 1 wherein said non-oxideelectrode is selected from the group consisting of TiN, TaN, WN, and W.3. A capacitor as claimed in claim 1 wherein said high dielectricconstant oxide dielectric material is selected from the group consistingof Al₂O₃, Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃.
 4. A capacitor comprising anon-oxide electrode selected from the group consisting of TiN, TaN, WN,and W, an upper surface of said non-oxide electrode being oxidized, ahigh dielectric constant oxide dielectric material adjacent said uppersurface of said non-oxide electrode, and an upper layer electrodeadjacent said high dielectric constant oxide dielectric material.
 5. Acapacitor as claimed in claim 4 wherein said high dielectric constantoxide dielectric material is selected from the group consisting ofAl₂O₃, Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃.
 6. A capacitor comprising anon-oxide electrode having an oxidized upper surface, a high dielectricconstant oxide dielectric material is selected from the group consistingof Al₂O₃, Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃ adjacent said upper surface ofsaid non-oxide electrode, and an upper layer electrode adjacent saidhigh dielectric constant oxide dielectric material.
 7. A capacitor asclaimed in claim 6 wherein said non-oxide electrode is selected from thegroup consisting of TiN, TaN, WN, and W.
 8. A capacitor comprising anon-oxide electrode selected from the group consisting of TiN, TaN, WN,and W, an upper surface of said non-oxide electrode having been oxidizedwith an O₃ gas plasma, a high dielectric constant oxide dielectricmaterial selected from the group consisting of Al₂O₃, Ta₂O₅ andBa_(x)Sr_((1−x))TiO₃ adjacent to said oxidized upper surface of saidnon-oxide electrode, and an upper layer electrode adjacent said highdielectric constant oxide dielectric material.